This invention relates to a pulse generation device and more particularly to a pulse generation device for newly generating a pulse based on a fly-back pulse generated in a television receiver.
FIG. 7 is a circuit diagram showing a conventional pulse generation device. A basic pulse which is used as the basis of a pulse to be created is input to an integrating circuit 22 via an input terminal 28 or a node N15. A comparing circuit 23 is supplied with a signal at the non-inverting input terminal or a node N16 thereof from the integrating circuit 22. Further, the inverting input terminal thereof is supplied with a reference voltage Vref9. The output of the comparing circuit 23 is connected to the input or an node N17 of a buffer circuit 24. The output of the buffer circuit 24 is connected to an output terminal 27 or a node N20 of the pulse generating device via a resistor R7 and further connected to the input of an integrating circuit 25. A signal from the integrating circuit 25 is input to the non-inverting input terminal or a node N18 of a comparing circuit 26. The inverting input terminal thereof is supplied with a reference voltage Vref10. An output of the comparing circuit 26 is supplied to the node N19 or the base of an NPN transistor Q15. The collector of the transistor Q15 is connected to the output terminal 27 of the pulse generating device and the emitter thereof is connected to a ground potential node GND.
FIG. 8 is a waveform diagram showing signal waveforms of various node portions, for illustrating the operation of the pulse generating device of FIG. 7. Slice levels by the reference voltages Vref9, Vref10 are shown together with the integrated waveforms at output nodes N16 and N18 of the respective integrating circuits 22 and 25. A waveform at the output node N17 of the comparing circuit 23 is a pulse waveform which is set at a high level in a period when the level of the integrated waveform is higher than the slice level of the reference voltage Vref9. A waveform at the output node N18 of the integrating circuit 25 is obtained by integrating an output of the comparing circuit 23 by use of a resistor R6 and capacitor C5 of the integrating circuit 25. A waveform at the output node N19 of the comparing circuit 26 is a pulse waveform which is set at a high level in a period when the level of the integrated waveform is higher than the reference voltage Vref10.
By adding together the output of the comparing circuit 23 and an output obtained by inverting the output of the comparing circuit 26 by use of the transistor Q15, a waveform of the node N20 can be obtained at the output terminal 27 of the pulse generating device. In the waveform of the node N20, a time width t9 ranging from the leading edge of the pulse input at the node N15 to the leading edge of the pulse at the node N20 can be determined by the reference voltage Vref9 and the time constant which is determined by a resistor R5 and capacitor C4 of the integrating circuit 22, and a time width t10 corresponding to the pulse width at the node N20 can be determined by the reference voltage Vref10 and the time constant which is determined by the resistor R6 and capacitor C5 of the integrating circuit 25.
Thus, in the prior art case, a new and necessary pulse is created by shaping the integrated waveform obtained by integrating the reference pulse by the capacitor C and resistor R by use of the slice level. Therefore, if the value of the capacitor C or resistor R varies, the integration time constant varies and the delay time corresponding to the time width t9 until the slice level is reached varies so that the created pulse phase at the node 20 will vary.
Since the integration time constant is kept unchanged even if the horizontal period of the reference pulse varies twice as shown in FIGS. 9A and 9B, time widths corresponding to t9, t10 are kept unchanged (t11=t13, t12=t14 in FIGS. 9A and 9B). Therefore, the rate of the time widths with respect to one horizontal period (=1 or =2) will vary. Therefore, in order to keep constant the rate of the time widths of t11 and t12 with respect to one horizontal period=1 and time widths of t13 and t14 with respect to one horizontal period=2, it is required to change the values of the capacitor C and resistor R, but this is impossible in practice.
This invention has been made to solve the above problem and an object of this invention is to provide a pulse generating device which can significantly reduce a variation in the phase of a newly created pulse waveform and in which the rate of the pulse width of the newly created pulse waveform with respect to a reference pulse width and the rate of the time width corresponding to the time delay of the created pulse waveform with respect to the reference pulse are precisely correspond to the period of an input pulse.